Discovery By UCSD Astronomers Poses A Cosmic Puzzle:
Can A 'Distant' Quasar Lie Within A Nearby Galaxy?

By Kim McDonald

An international
team of astronomers has discovered within the heart of a nearby
spiral galaxy a quasar whose light spectrum indicates that it
is billions of light years away. The finding poses a cosmic
puzzle: How could a galaxy 300 million light years away contain
a stellar object several billion light years away?

The team’s findings,
which were presented today in San Diego at the January meeting
of the American Astronomical Society and which will appear in
the February 10 issue of the Astrophysical Journal,
raise a fundamental problem for astronomers who had long assumed
that the “high redshifts” in the light spectra of
quasars meant these objects were among the fastest receding
objects in the universe and, therefore, billions of light years
away.

“Most people
have wanted to argue that quasars are right at the edge of the
universe,” said Geoffrey Burbidge, a professor of physics
and astronomer at the University of California at San Diego’s
Center for Astrophysics and Space Sciences and a member of the
team. “But too many of them are being found closely associated
with nearby, active galaxies for this to be accidental. If this
quasar is physically associated with this galaxy, it must be
close by.”

Astronomers generally
estimate the distances to stellar objects by the speed with
which they are receding from the earth. That recession velocity
is calculated by measuring the amount the star’s light
spectra is shifted to the lower frequency, or red end, of the
light spectrum. This physical phenomenon, known as the Doppler
Effect, can be experienced by someone standing near train tracks
when the whistle or engine sounds from a moving train becomes
lower in pitch, or sound frequency, as the train travels past.

Astronomers have
used redshifts and the known brightness of stars as fundamental
yardsticks to measure the distances to stars and galaxies. However,
Burbidge said they have been unable to account for the growing
number of quasi-stellar objects, or quasars—intense concentrations
of energy believed to be produced by the swirling gas and dust
surrounding massive black holes—with high redshifts that
have been closely associated with nearby galaxies.

“If it weren’t
for this redshift dilemma, astronomers would have thought quasars
originated from these galaxies or were fired out from them like
bullets or cannon balls,” he added.

The discovery reported
by the team of astronomers, which includes his spouse, E. Margaret
Burbidge, another noted astronomer and professor of physics
at UCSD, is especially significant because it is the most extreme
example of a quasar with a very large redshift in a nearby galaxy.

“No one has
found a quasar with such a high redshift, with a redshift of
2.11, so close to the center of an active galaxy,” said
Geoffrey Burbidge.

Margaret Burbidge,
who reported the team’s finding at the meeting, said the
quasar was first detected by the ROSAT X-ray satellite operated
by the Max-Planck Institute for Astrophysics in Garching, Germany
and found to be closely associated with the nucleus of the spiral
galaxy NGC 7319. That galaxy is unusual because it lies in a
group of interacting galaxies called Stephan’s Quintet.

Using a three-meter
telescope operated by the University of California at Lick Observatory
in the mountains above San Jose and the university’s 10-meter
Keck I telescope on Mauna Kea in Hawaii, she and her team measured
the redshifts of the spiral galaxy and quasar and found that
the quasar appears to be interacting with the interstellar gas
within the galaxy.

Because quasars and
black holes are generally found within the most energetic parts
of galaxies, their centers, the astronomers are further persuaded
that this particular quasar resides within this spiral galaxy.
Geoffrey Burbidge added that the fact that the quasar is so
close to the center of this galaxy, only 8 arc seconds from
the nucleus, and does not appear to be shrouded in any way by
interstellar gas make it highly unlikely that the quasar lies
far behind the galaxy, its light shining through the galaxy
near its center by “an accident of projection.”

“If this quasar
is close by, its redshift cannot be due to the expansion of
the universe,” he adds. “If this is the case, this
discovery casts doubt on the whole idea that quasars are very
far away and can be used to do cosmology.”

Other members of
the team, besides Geoffrey and Margaret Burbidge, included Vesa
Junkkarinen, a research physicist at UCSD; Pasquale Galianni
of the University of Lecce in Italy; and Halton Arp and Stefano
Zibetti of the Max-Planck Institute for Astrophysics in Garching,
Germany.